As it is generally known, labeling machines are used to apply labels to containers or articles of all sort. Typically used with beverage bottles or vessels are tubular labels (commonly called “sleeve labels”), which are obtained by:                cutting the web unwound from a supply roll into a plurality of rectangular or square labels of a heat-shrinkable material;        bending each label in a cylindrical configuration such that the opposite vertical edges overlap one another; and        welding the overlapped edges of each cylindrical label.        
In particular, a labeling machine is known comprising a carousel mounted to rotate about a substantially vertical first longitudinal axis, and having a number of carrier units, each for feeding a respective article between an input station, where the articles are fed onto the conveyor wheel, and an output station, where the articles are fed off the carousel.
Each carrier unit comprises a tubular upright fixed to the carousel, and having a second longitudinal axis substantially parallel to the first axis; a supporting spindle, which engages the upright in rotary and axially-sliding manner, has a top end defining a substantially horizontal supporting surface for a respective article, and is bounded externally by a cylindrical lateral surface connectable to a pneumatic suction device; and a top retaining member, which cooperates with the spindle to keep the article upright on the supporting surface.
The spindle is movable axially between a lowered position—in which the spindle is substantially housed inside the upright, so the carrier unit can receive an article at the input station and release the article at the output station—and a raised position—in which the spindle projects from the upright, so the lateral surface of the spindle can receive and retain a label.
The spindle also rotates about the second axis, to wind the label completely about the spindle into a tubular configuration having a longitudinal overlap defined by superimposed portions of the label, and which is heat sealed longitudinally by a heat-seal bar associated with the carrier unit.
Once the label is heat sealed, and by combining the downward movement of the spindle inside the upright with deactivation of the pneumatic suction device, the label is released from the lateral surface of the spindle, is retained on the upright by a top annular edge of the upright, and is engaged in sliding manner by a respective article.
The articles coming off the carousel are fed, substantially upright, by a linear conveyor device through a heating device to heat-shrink the labels about the articles.
Because the labels are fed through the heating device still in contact with a supporting surface of the conveyor device, known labeling machine of the above type have several drawbacks, mainly due to not allowing selective control of the position of the labels along the articles, and as such as are fairly inflexible.
In order to overcome the above drawback, a labeling machine is known from WO-A-2011/114358, in the name of the same Applicant.
In detail, the conveyor device of this labeling machine comprises:                a bottom belt which defines a substantially horizontal supporting surface for the articles coming out from the carousel;        a top belt which is separated from the supporting surface by a distance substantially equal to the height of the article;        a positioning unit which interacts with the articles travelling onto the bottom conveyor and is adapted to position the tubular labels in a given final position; and        a stop device which interacts with the articles upstream of positioning unit and is adapted to arrest the labels in respective given final positions relative to corresponding articles.        
In detail, the bottom belt feeds articles with respective labels successively and continuously through positioning unit, which comprises a pair of first brushes and a pair of brushes.
Both first brushes and second brushes counter-rotate relative to each other and are arranged on opposite sides of the articles travelling onto conveyor device.
Second brushes are arranged downstream of first brushes, proceeding according to the travelling direction of the articles onto the conveyor device.
As articles travel onto conveyor, labels are first raised by first brushes from an initial lowered position, in which the labels substantially contact the supporting surface of the bottom branch to an intermediate position, in which the labels substantially contact the top branch; afterwards, labels are lowered by second brushes from the intermediate position to the given final position in which they are arrested by the stop device.
The stop device substantially comprises two endless conveyors arranged on opposite lateral sides of the conveyor device and which have respective branches cooperating with opposite side of the label to arrest this labels in the final given position.
The Applicant has found that the above described solution can be improved, especially as regard to reliability, precision and speed of the positioning of the labels in the given final position.
A need is felt within the industry to obtain labeling machine which can apply tubular labels either to the full body of the containers or to only a portion of the outer surface of relative containers, and which overcomes the above drawback in a simple and economic way.
JP-A-2011-213377 discloses a picker for picking labels. In detail, the picker comprises two members formed to match the diameters of the article. The two members are rotated about an axis between an open and a closed by an opening/closing mechanism, and are raised and lowered along this axis. The inner surface of each member of the picker comprises a plurality of a suction holes connected to a vacuum source.